JP7587487B2 - Optical fiber communication system and optical transmission device - Google Patents

Description

The present invention relates to an optical fiber communication system and optical transmission equipment that improves wireless quality at area boundaries.

Various studies have been conducted to improve the quality of wireless communication in optical fiber communication systems.

As a technology for improving wireless quality, Non-Patent Document 1 discloses technology related to a Centralized radio access network (C-RAN) architecture in which a Baseband unit (BBU) and a Distributed unit (DU) having higher layer functions of a wireless base station are placed on the accommodating station side, and a Remote radio head (RRH) and a Remote unit (RU) having lower layer functions are placed on the Antenna (ANT) installation site. In a C-RAN, it is possible to improve wireless quality by centrally controlling and coordinating the operation of multiple wireless base stations placed in the same accommodating station.

Non-Patent Document 2 also discloses an optical access method that uses a Point to Multipoint (PtMP) architecture in a Wavelength division multiplexing passive optical network (WDM-PON) configuration as a Mobile fronthaul (MFH) based on analog radio over fiber (RoF) technology, and effectively utilizes a single access fiber to accommodate multiple ANT sites.

Patent Document 1 also discloses an optical access method that constructs a PtMP architecture using intermediate frequency over fiber (IFoF) links and cascaded connections of IFoF and RoF links as a Mobile fronthaul (MFH) based on analog RoF technology, making effective use of a single access fiber to accommodate multiple ANT sites.

TTC Technical Report TR-1079 Technical Report on Optical Access in the Fronthaul of 5th Generation Mobile Communication Systems 10.1109/JLT.2019.2923245/Experimental Demonstration of a WDM-RoF Based Mobile Fronthaul With f-OFDM Signals by Using Directly Modulated 3s-DBR Laser

JP 2019-212983 A

However, in Non-Patent Document 1, when a wireless user terminal is located at the edge between cells of different accommodating stations, it becomes difficult to improve wireless signal quality by inter-base station cooperative operation (such as Multiple-Input Multiple-Output (MIMO) between different antenna sites), which is a feature of Centralized radio access network (C-RAN).

In addition, the system configuration required to realize the technology in Non-Patent Document 2 is complex, and many additional access fibers are required. In addition, there are concerns that the increased distance of the access fibers will lead to increased costs and longer construction times.

The present invention was made in consideration of these circumstances, and aims to provide an optical fiber communication system and optical transmission device that are simple and economical optical access systems.

(1) In order to achieve the above object, the present invention employs the following means. That is, the optical fiber communication system of the present invention is an optical fiber communication system composed of a plurality of OLTs (Optical Line Terminals) each having a plurality of ONUs (Optical Network Units) thereunder, and is characterized in that it comprises a plurality of relay stations provided between each of the OLTs and each of the ONUs, and relay optical fibers optically connecting each of the relay stations, and each of the OLTs transmits signals to ONUs under the control of other OLTs using the relay optical fibers.

(2) In the optical fiber communication system of the present invention, each OLT includes a wavelength controller for controlling a wavelength when optically communicating with a subordinate ONU, and when the first OLT determines, based on location information of a terminal device communicating with a subordinate ONU, that the terminal device is communicating with an ONU outside the communication area of each subordinate ONU, the first OLT requests a second OLT that accommodates the ONU outside the communication area to switch to an outside-area mode in which communication is performed using the relay optical fiber, and the second OLT If the request is permitted, the first OLT and the second OLT transition to the outside-area mode, and the wavelength controller of the first OLT or the wavelength controller of the second OLT notifies the ONU under the control of the second OLT that should transition to the outside-area mode of the wavelength to be used in the outside-area mode, and the terminal device communicates with the first OLT via the ONU that transitioned to the outside-area mode and the relay optical fiber.

(3) In the optical fiber communication system of the present invention, the first OLT uses the relay optical fiber to transmit signals between any of the ONUs under the control of the second OLT at a wavelength assigned for inter-relay station transmission.

(4) In the optical fiber communication system of the present invention, each OLT is provided with an IF controller that multiplexes a radio signal into an optical signal to control the frequency when performing IF/OF communication with the subordinate ONU, and when the third OLT determines, based on the position information of a terminal device communicating with the subordinate ONU, that the terminal device is communicating with an ONU outside the communication area of each subordinate ONU, it requests the fourth OLT that accommodates the ONU outside the communication area to switch to an outside area mode in which communication is performed using the relay optical fiber. If the fourth OLT permits the request, the third OLT and the fourth OLT transition to the outside-area mode, and the IF controller of the third OLT or the IF controller of the fourth OLT notifies the ONU that should transition to the outside-area mode, among the ONUs under the fourth OLT, of the frequency to be used in the outside-area mode, and the terminal device communicates with the third OLT via the ONU that transitioned to the outside-area mode and the relay optical fiber.

(5) In the optical fiber communication system of the present invention, the third OLT uses the relay optical fiber to perform IFoF communication with any of the ONUs under the control of the fourth OLT at a frequency assigned for transmission between relay stations.

(6) In the optical fiber communication system of the present invention, each OLT includes an OLT-side IF controller that multiplexes a radio signal into an optical signal and controls the frequency when performing IFoF communication with the subordinate ONU, and each relay station includes a relay station-side IF controller that is controlled by each OLT-side IF controller. When the fifth OLT determines, based on location information of a terminal device communicating with a subordinate ONU, that the terminal device is communicating with an ONU outside the communication area of each subordinate ONU, the fifth OLT uses the relay optical fiber to communicate with the sixth OLT that accommodates the ONU outside the communication area. When the sixth OLT requests to transition to an outside-area mode in which the sixth OLT allows the request, the fifth OLT and the sixth OLT transition to the outside-area mode, and the OLT-side IF controller of the fifth OLT and the OLT-side IF controller of the sixth OLT notify the relay-side IF controller of the relay station under each of the subordinates of the frequency to be used in the outside-area mode, and the terminal device communicates with the fifth OLT via the ONU under the sixth OLT that has transitioned to the outside-area mode and the relay optical fiber.

(7) The optical transmission device of the present invention is an OLT applied to an optical fiber communication system, and is characterized in that it includes a wavelength controller that controls the wavelength when optically communicating with a subordinate optical network device, and when wavelength information indicating the wavelength used by the subordinate optical network device of the other optical transmission device is notified from the other optical transmission device, it controls the wavelength controller included in the device itself so that the subordinate optical network device uses the wavelength indicated in the notified wavelength information.

(8) The optical transmission device of the present invention is an optical transmission device applied to an optical fiber communication system, and is characterized in that it includes an IF controller that controls the frequency when multiplexing a radio signal into an optical signal and performing IFoF communication with a subordinate optical network device, and when frequency information indicating the frequency used by an optical network device subordinate to the other optical transmission device is notified from the other optical transmission device, it controls the IF controller included in the device itself so that the subordinate optical network device or the IF controller on the relay station side uses the frequency indicated in the notified frequency information.

The present invention makes it possible to improve the quality of wireless communications near area boundaries. It also makes it possible to build an optical fiber communication system with a simple and economical structure that keeps optical fiber costs and installation time short.

1 is a diagram showing a schematic configuration of an optical fiber communication system according to each embodiment. 1 is a diagram showing an overview of an optical fiber communication system according to a first embodiment. FIG. 13 is a diagram showing how the ANT to which the UE is connected changes. FIG. 2 is a diagram illustrating a schematic configuration of a communication station CO-B according to the first embodiment. FIG. 4 is a diagram illustrating an example of wavelength allocation in the first embodiment. FIG. 2 is a diagram illustrating a schematic configuration of a relay station RN-B according to the first embodiment. 2 is a diagram illustrating a schematic configuration of a relay station RN-A according to the first embodiment. FIG. 1A and 1B are diagrams illustrating a schematic configuration of each antenna site during normal operation (no communication outside the area) and the positional relationship between each antenna site and each UE. 13A and 13B are diagrams showing a schematic configuration of each antenna site during switching operation (with communication outside the area) and the positional relationship between each antenna site and each UE. 11 is a table showing an example of a correspondence between UE location information and each port output wavelength. 11 is a table showing an example of a correspondence between UE location information and each port output wavelength. FIG. 11 is a diagram showing position conditions for route switching. 1A and 1B are diagrams illustrating the structures of a PtP fiber and a Ring fiber. FIG. 13 is a diagram showing an overview of an optical fiber communication system according to a second embodiment. FIG. 11 is a diagram illustrating a schematic configuration of a communication station CO-B according to a second embodiment. FIG. 11 is a diagram illustrating an example of wavelength allocation in the second embodiment. FIG. 11 is a diagram illustrating a schematic configuration of a relay station RN-B according to a second embodiment. FIG. 11 is a diagram illustrating a schematic configuration of a relay station RN-A according to a second embodiment. 1A and 1B are diagrams showing a schematic configuration of each antenna site and the positional relationship between each antenna site and each UE. FIG. 13 is a diagram showing an overview of an optical fiber communication system according to a third embodiment. FIG. 13 is a diagram illustrating a schematic configuration of a communication station CO-B according to a third embodiment. FIG. 13 is a diagram illustrating an example of an arrangement of IFoF transmission frequencies between CO and RN in the third embodiment. FIG. 13 is a diagram illustrating a schematic configuration of a relay station RN-B according to a third embodiment. FIG. 13 is a diagram illustrating a schematic configuration of a relay station RN-A according to a third embodiment. FIG. 13 is a diagram illustrating an example of an arrangement of IFoF transmission frequencies between relay stations (RN-A, RN-B) in the third embodiment. A figure showing an example of the arrangement of IFoF transmission frequencies between RN-B and an ONU/ANT site in the third embodiment. 1A and 1B are diagrams illustrating a schematic configuration of each antenna site during normal operation (no communication outside the area) and the positional relationship between each antenna site and each UE. 13A and 13B are diagrams showing a schematic configuration of each antenna site during switching operation (with communication outside the area) and the positional relationship between each antenna site and each UE. 11 is a table showing an example of a correspondence between UE location information and each port output IF. 11 is a table showing an example of a correspondence between UE location information and each port output IF. FIG. 13 is a diagram showing an overview of an optical fiber communication system according to a fourth embodiment. FIG. 13 is a diagram illustrating a schematic configuration of a communication station CO-B according to a fourth embodiment. FIG. 13 is a diagram illustrating an example of an arrangement of IFoF transmission frequencies between CO and RN in the fourth embodiment. FIG. 13 is a diagram illustrating a schematic configuration of a relay station RN-B according to a fourth embodiment. FIG. 13 is a diagram illustrating a schematic configuration of a relay station RN-A according to a fourth embodiment. FIG. 13 is a diagram illustrating an example of an arrangement of IFoF transmission frequencies between relay stations (RN-A, RN-B) in the fourth embodiment. A figure showing an example of the arrangement of IFoF transmission frequencies between RN-B and an ONU/ANT site in the fourth embodiment. 13A and 13B are diagrams illustrating a schematic configuration of each antenna site and a positional relationship between each antenna site and each UE in a fourth embodiment. FIG. 13 is a diagram showing an overview of an optical fiber communication system according to a fifth embodiment. FIG. 13 is a diagram illustrating a schematic configuration of a communication station CO-B according to a fifth embodiment. FIG. 13 is a diagram illustrating an example of an arrangement of IFoF transmission frequencies between CO and RN in the fifth embodiment. FIG. 13 is a diagram illustrating a schematic configuration of a relay station RN-B according to a fifth embodiment. FIG. 13 is a diagram illustrating a schematic configuration of a relay station RN-A according to a fifth embodiment. FIG. 13 is a diagram illustrating an example of an arrangement of IFoF transmission frequencies between relay stations (RN-A, RN-B) in the fifth embodiment. A figure showing an example of the arrangement of IFoF transmission frequencies between RN-B and an ONU/ANT site in the fifth embodiment. 1A and 1B are diagrams illustrating a schematic configuration of each antenna site during normal operation (no communication outside the area) and the positional relationship between each antenna site and each UE. 13A and 13B are diagrams showing a schematic configuration of each antenna site during switching operation (with communication outside the area) and the positional relationship between each antenna site and each UE. 11 is a table showing an example of correspondence between UE location information and input/output IFs in each TRx.

The inventors noticed that wireless quality becomes unstable near area borders in optical fiber communication systems, and discovered that wireless quality can be improved near area borders by connecting relay stations with optical fiber, which led to the invention.

That is, it is an optical fiber communication system consisting of a plurality of OLTs (Optical Line Terminals) each having a plurality of ONUs (Optical Line Terminals) under its control, and is characterized in that it comprises a plurality of relay stations respectively provided between each of the OLTs and each of the ONUs, and relay optical fibers optically connecting each of the relay stations, and each of the OLTs transmits signals to ONUs under the control of other OLTs using the relay optical fibers.

As a result, the inventors have been able to realize a simple and economical optical fiber communication system that improves the quality of wireless communication near area boundaries and that can reduce the cost of optical fiber and the time required to lay and install the optical fiber. The following describes in detail an embodiment of the present invention with reference to the drawings.

First, an overview of the optical fiber communication system common to each embodiment will be described. Figure 1 is a diagram showing the schematic configuration of the optical fiber communication system according to each embodiment.

The optical fiber communication system 1 is a PON (Passive Optical Network) consisting of optical transmission equipment (OLT (Optical Line Terminal) 11, 21) and multiple optical network equipment (ONU (Optical Line Terminal) 15, 25). It has relay stations (RN: Remote node) 13, 23 to accommodate base station antenna groups 16, 26 optically connected to accommodation stations CO-A and CO-B, respectively, in a Point to multi-point (PtMP) manner by effectively utilizing a single access fiber. The relay stations 13, 23 use passive components such as AWG and WDM CPL to assign optical signal transmission destination sites by wavelength. In this specification, the relay station is also referred to as a remote node (RN) or aggregation station. The accommodation stations (CO: Central Office) in adjacent areas are connected by an upper network.

Furthermore, in the optical fiber communication system according to this embodiment, relay stations in adjacent areas are connected by relay optical fibers 31. By optically connecting the relay stations, base station antennas (antenna sites) under the control of the accommodation stations CO-A/B can communicate via the following routes.
(1) Base station antenna ⇔ relay station A/B ⇔ relay station B/A ⇔ accommodation station CO-B/A ⇔ base station A/B
(2) Base station antenna ⇔ relay station A/B ⇔ accommodation station A/B (normal connection configuration)

In other words, until now, communication was only possible via route (2), but by connecting relay stations in adjacent areas (RN-A⇔RN-B) with relay optical fiber 31, it will also be possible to communicate via the route (1) from base station antenna⇔relay station A⇔relay station B⇔accommodating station CO-B⇔base station A, or from base station antenna⇔relay station B⇔relay station A⇔accommodating station CO-A⇔base station B.

In an optical fiber communication system constructed in this way, the present invention uses wavelength controllers 17, 27 or IF controllers 19, 29 to enable an OLT to switch the ONU with which it is communicating, or to communicate simultaneously with two ONUs in different areas, based on the reception conditions of user equipment (UE) position information (which may be wireless communication quality from each Antenna (ANT) at the UE or a base station) that changes with time.

In this way, a user equipment (UE) that communicates with a base station (BS) can perform wireless communication with both a part of a group of cells optically connected to a central office-A (CO-A) and a part of a group of cells optically connected to another central office CO-B, thereby improving the wireless quality at the cell edge. Note that "cell" may be replaced with "base station antenna (ANT)."

It is also possible to optically connect relay station A (RN-A) and relay station B (RN-B) directly to accommodation station CO-B and accommodation station CO-A, respectively. However, optically connecting relay stations (RN-A⇔RN-B) rather than optically connecting relay station RN-A and relay station RN-B to accommodation station CO-B and accommodation station CO-A, respectively, reduces optical fiber costs and shortens the fiber installation period, allowing the construction of a simple and economical optical fiber communications system.

The following configuration patterns are possible for implementing the above-described system.
[1] Connection method between OLT and ONU outside the area (1) Switching (a connection method in which a connection with an ONU within the area is interrupted when a connection with an ONU outside the area is established)
(2) Always-on connection (a connection method that allows simultaneous connection to ONUs outside the area and ONUs inside the area at all times)

[2] Methods for implementing PtMP (1) WDM-PON (Wavelength Division Multiplexing-Passive Optical Network): This changes the location of the base station antenna by switching the optical wavelength of the station and antenna site based on the terminal's location information (which can be each Antenna (ANT) at the UE or the wireless communication quality from the base station).
(2) Cascade connection: Based on the location information of the terminal (which may be each Antenna (ANT) in the UE or the wireless communication quality from the base station), the IF for IFoF transmission is changed at the accommodating station and antenna site to change the accommodation of the base station antenna. Alternatively, based on the location information of the terminal, the IF for IFoF transmission is changed at the relay station to change the accommodation of the base station antenna.

[3] Additional access fiber configuration (1) Additional PtP (Point to Point) fiber configuration (2) Additional Ring fiber configuration

The configurations combining [1] and [2] will be specifically described in each embodiment below. [3] The additional access fiber configuration will be described in the PtP fiber additional configuration, but the same applies to the Ring fiber additional configuration.

In this specification, the direction from the OLT of the accommodating station to the relay station or antenna site is referred to as downlink, and the direction from the antenna site or relay station to the OLT of the accommodating station is referred to as uplink.

In the following, in order to make the present invention easier to understand, each embodiment will be described focusing on two adjacent areas consisting of two accommodating stations and their subordinate base station antennas and UEs, but it goes without saying that the same applies when there are multiple adjacent accommodating stations. Furthermore, the description will focus on the area of accommodating station CO-B, but it goes without saying that the same applies to the area of accommodating station CO-A and the areas of other adjacent accommodating stations.

[First embodiment]
The configuration patterns in this embodiment are as follows.
[1] Connection method between OLT and outside area ONU: Switching method [2] PtMP realization method: WDM-PON
[3] Additional access fiber configuration: PtP fiber additional configuration

First, an overview of the optical fiber communication system according to this embodiment will be described. Fig. 2 is a diagram showing an overview of the optical fiber communication system according to the first embodiment. Fig. 3 is a diagram showing how the ANT to which the UE is connected changes (beam forming #1 -> beam forming #2) depending on the area location of the UE. Fig. 3 shows, as an example, a case in which an environment in which the UE communicates with four ANTs simultaneously, but is not limited to this.

A relay station is provided to accommodate the base station antenna groups optically connected to the CO-A and CO-B, making effective use of a single access fiber, and to accommodate Point to multi-point (PtMP) connections. The relay station uses passive components such as AWG and WDM CPL to allocate the optical signal's destination site by wavelength.

Based on the location of the user terminal, which changes with time, the OLT and ONU change the settings of the wavelength used, and each base station antenna communicates with the accommodating station CO-A or CO-B. Although wavelength changes have been described as triggered by the location information of the user terminal, wavelength changes may also be triggered by other information held by the user terminal or base station equipment (such as wireless communication quality information between the antenna/base station and the user terminal). The configuration of each device and the wavelength change procedure are explained in detail below.

[Configuration of each device in the optical fiber communication system]
Each device constituting the optical fiber communication system according to this embodiment will be described.
(Accommodation station)
4 is a diagram showing a schematic configuration of a accommodating station CO-B according to the first embodiment. The accommodating station CO-B communicates not only with ONU#1-1 in the CO-B area, but also with ONU#1-1' in the CO-A area depending on the time. The accommodating station CO-B includes a BS, an OLT, and a wavelength controller.

A base station (BS) has a BS pool consisting of multiple BSs or BS functions, and connection ports (BS Ports) for multiple BSs or BS functions. Figure 4 shows an example configuration assuming m base stations (number of base station functions) and n number of connection ports for each base station.

The OLT is equipped with a TRx (Transceiver), AWG (Array Waveguide Gratings) for DL (Downlink)/UL (Uplink), and a WDM CPL (Wavelength division multiplexing Coupler). TRx#1-1 is connected to a wavelength controller and receives information about the wavelengths used by the OLT and ONUs from the wavelength controller. TRx#1-1 then outputs the wavelengths used by the OLT and ONUs based on the received wavelength information. Regarding the notation of wavelength λ in Figure 4, those without "'" indicate wavelengths for ONUs under CO-B, and those with "'" indicate wavelengths for ONUs under CO-A. This is the same in other figures.

It is assumed that TRx#1-1 outputs either λ _d1-1 (wavelength under CO-B) or λ _d1-1 ' (wavelength under CO-A). For example, when communicating with ONU#1-1 under CO-B, the wavelength λ _d1-1 is output, and when communicating with ONU#1-1' under CO-A, the wavelength λ _d1-1 ' is output. Possible methods for selecting the wavelength to be output in TRx#1-1 include selecting the wavelength with a tunable LD (Laser Diode) or preparing two LDs with different wavelengths and outputting one of them. In addition, if it is necessary to communicate with other ONUs (ONUs other than ONU#1-1) in the CO-A area, multiple TRxs with the function of TRx#1-1 are required.

Figure 5 shows an example of wavelength allocation in the first embodiment. Figure 5(a) shows a method of allocating wavelengths grouped together by antenna site and transmission direction. Figure 5(b) shows a method of allocating wavelengths grouped together by transmission direction. In this embodiment, in order to perform wavelength multiplexing transmission in which light of different wavelengths is transmitted over a single optical fiber, wavelengths are allocated in the AWG and WDM CPL as shown in Figure 5, for example, to transmit light of different wavelengths.

The basic equipment configuration of the CO-A accommodating station is the same as that of the CO-B accommodating station. However, because the wavelengths used are different from those of the CO-B accommodating station, the wavelength notation is reversed in Figure 4, with the λ notation marked with an "'" and the one without. Also, because the CO-A accommodating station communicates with the relay station RN-A, it is written as "From/To RN-A."

(Relay station)
Fig. 6A is a diagram showing a schematic configuration of a relay station RN-B according to the first embodiment. Fig. 6B is a diagram showing a schematic configuration of a relay station RN-A according to the first embodiment. Since the configurations of the relay station RN-B and the relay station RN-A are the same, the configuration of the relay station RN-B will be described with reference to Fig. 6A.

Repeater station RN-B is connected to ONUs as well as to relay station RN-A in an adjacent area via relay optical fiber. The AWG and WDM CPL allocate the destination site of the optical signal by wavelength. AWG for DL_A and AWG for DL_B are used to WDM multiple downstream transmission signals transmitted between RN-A and RN-B. Therefore, they are not necessary when transmitting only one wavelength. AWG for UL_A and AWG for UL_B are used to WDM multiple upstream transmission signals transmitted between RN-A and RN-B. Therefore, they are not necessary when transmitting only one wavelength.

In relay station RN-B, in addition to the conventional PON system configuration, the gray parts in Figure 6A are added as new configurations, but both are simple configurations that can be configured using only passive components.

(Antenna site)
The antenna site consists of an ONU and an ANT. The ONU is equipped with a WDM-CPL, an O/E, an E/O, and a Circulator, and transmits the wavelength transmitted from the relay station to the UE. The Circulator is a component that separates upstream and downstream transmissions, and may be a switch, etc. Also, the Circulator may not be included in the ONU configuration and may be provided externally.

Figure 7(a) is a diagram showing the schematic configuration of each antenna site during normal operation (no outside-area communication). Figure 7(b) is an image diagram showing the positional relationship between each antenna site and each UE during normal operation (no outside-area communication). As shown in Figures 7(a) and (b), during normal operation, outside-area communication is not performed, and communication is performed within the same area.

For example, UE#2 communicates with antenna sites (ONU#1-1, ONU#1-2, ONU#1-3, ONU#1-4) in the vicinity of UE#2 and in the CO-B area, and wavelengths are transmitted along the communication path from the antenna sites (ONU#1-1, ONU#1-2, ONU#1-3, ONU#1-4) ⇔ relay station B ⇔ accommodating station B, so that in downstream transmission, wavelength λ _d1-1 (wavelength under CO-B) is input to ONU#1-1, and in upstream transmission, wavelength λ _u1-1 (wavelength under CO-B) is output from ONU#1-1. Similarly, UE#1-1' communicates with antenna sites (ONU#1-1', ONU#1-2', ONU#1-3', ONU#1-4') in the vicinity of UE#1 and in the CO-A area, and wavelengths are transmitted along the communication path from the antenna sites (ONU#1-1', ONU#1-2', ONU#1-3', ONU#1-4') ⇔ relay station A ⇔ accommodating station A, so that in downstream transmission, wavelength λ _d1-1 ' (wavelength under CO-A) is input to ONU#1-1', and in upstream transmission, wavelength λ _u1-1 ' (wavelength under CO-A) is output from ONU#1-1'.

Figure 8 (a) is a diagram showing the schematic configuration of each antenna site during switching operation (with outside-area communication). Figure 8 (b) is an image diagram showing the positional relationship between each antenna site and each UE during switching operation (with outside-area communication). When switching operation is performed, outside-area communication is performed.

For example, when UE#2 moves near the boundary of the area, the antenna site with which UE#2 communicates changes from ONU#1-1, ONU#1-2 to ONU#1-1', ONU#1-2', and communication outside the area is performed. UE#2 communicates with antenna sites (ONU#1-1', ONU#1-2', ONU#1-3, ONU#1-4) near the boundary of the area. The changed antenna site (ONU#1-1', ONU#1-2') transmits wavelengths on the communication path from antenna site (ONU#1-1', ONU#1-2')⇔relay station A⇔relay station B⇔accommodation station CO-B⇔base station A, so in downstream transmission, wavelength λ _d1-1 ' (wavelength under CO-A) is input to ONU#1-1', and in upstream transmission, wavelength λ _u1-1 (wavelength under CO-B) is output from ONU#1-1'. The same is true for ONU#1-2'. On the other hand, ONU#1-1 and ONU#1-2, which no longer communicate with UE#2, may stop inputting and outputting wavelengths, or change the wavelength for upstream transmission to wavelength λ _u1-1 ' for CO-A, and transmit the wavelength via the communication path from antenna site (ONU#1-1, ONU#1-2) ⇔ relay station B ⇔ relay station A ⇔ accommodating station CO-A ⇔ base station B.

[Procedure for changing wavelength settings]
Next, a method for controlling antenna sites in use in this embodiment will be described with reference to Figures 2 to 8. As described above, the accommodating stations CO-A and CO-B are accommodating stations whose coverage areas are adjacent to each other, and the areas under the accommodating stations CO-A and CO-B are operated based on different wavelength bands (for example, wavelength group A and wavelength group B).

(1) In the area of CO-B (wavelength group B), first, the location information of UE#2 transmitted from UE#2 to the BS or mobile core of the accommodating station CO-B is input to the wavelength controller of the OLT. The method of inputting the location information of UE#2 to the wavelength controller includes, but is not limited to, the following two methods.
(i) The BS of the accommodating station CO-B directly reads the location information from UE#2, and inputs the read location information of UE#2 to the wavelength controller.
(ii) The location information management server in the upper network reads the location information of UE#2, and inputs the read location information of UE#2 to the wavelength controller.

The wavelength controller holds in advance a correspondence table between UE location information and each port output wavelength. Here, we explain the correspondence table between UE location information and each port output wavelength of the OLT and ONU.

9 and 10 are tables showing an example of the correspondence between UE location information and each port output wavelength. FIG. 9(a) is a table summarizing information on wavelengths output to OLT Port#1-1 in CO-B, and FIG. 9(b) is a table summarizing information on wavelengths output to OLT Port#1-1' in CO-A. For example, FIG. 9(a) shows that when the location information (Location information) of UE#2 is "1" (normal operation mode), the wavelength (OLT output wavelength) used in downstream transmission is "λ _d1-1 " and the wavelength (ONU output wavelength) used in upstream transmission is "λ _u1-1 ", and when the location information (Location information) of UE#2 is "101" (outside area operation mode), the wavelength (OLT output wavelength) used in downstream transmission is "λ _d1-1 '" and the wavelength (ONU output wavelength) used in upstream transmission is "λ _u1-1 ".

On the other hand, when UE#2 is in out-of-area operation mode, CO-A stops outputting wavelengths to the ONUs (ONU#1-1', ONU#1-2') under CO-A and interrupts communication. Therefore, in the out-of-area operation mode in FIG. 9(b), the wavelength used in downstream transmission (OLT output wavelength) is set to "No output" and the wavelength used in upstream transmission (ONU output wavelength) is set to "-". Also, in order to make effective use of resources, in the out-of-area operation mode, CO-A may set the wavelength used in downstream transmission (OLT output wavelength) to "λ d1-1 " and the wavelength used in upstream transmission (ONU output wavelength) to "λ u1-1 '" as shown in FIG. 10(b) so as to communicate with the ONUs (ONU# _1-1 , ONU# _1-2 ) under CO-B.

(2) After inputting the location information of UE#2 into the wavelength controller, the OLT checks the correspondence table. If communicating with an ONU outside the area of accommodating station CO-B (for example, ONU#1-1' in CO-A's area), the OLT sends a request for communication outside the area (including the permitted period and time (timing) for communication, the wavelength to be used, information on wavelengths that will no longer be used due to changing the wavelength to be used, etc.) to the OLT (wavelength controller) in CO-A's area that accommodates the ONU outside the area (ONU#1-1').

(3) The OLT in the CO-A area that receives the request for out-of-area communication returns the availability and the permitted time (timing) to the sending OLT (OLT in the CO-B area). Regarding the availability, for example, a rule may be determined in advance that indicates that the request can be accepted if there is a reply from the OLT that is the destination of the request within a certain period of time, and that the request cannot be accepted if there is no reply within the certain period of time, but the rules are not limited to this.

(4) The OLT (wavelength controller) that has received permission for communication outside its area switches the output wavelength of the OLT based on the wavelength controller's correspondence table during the permission period (time). Then, the OLT that issued permission for communication outside its area (OLT in CO-A's area) stops outputting its own wavelength during the permission period based on the wavelength controller's correspondence table.

(5) The OLT (OLT of CO-B) that issued the out-of-area communication request sends a wavelength change command to the out-of-area ONU (ONU #1-1' in the CO-A area) that is the communication destination of that port (Port) along with changing the wavelength of its own Tx (Transmitter). Note that in steps (4) and (5), the OLT (OLT of CO-A) that issued the out-of-area communication permission may also issue a wavelength change command to the subordinate ONU (the ONU (ONU of CO-A) that is out of the area from the perspective of the OLT (OLT of CO-B) that issued the out-of-area communication request) before stopping the output of its own wavelength.

(6) The outside-area ONU (ONU of CO-A) that received the wavelength change command changes its output wavelength based on the information contained in the wavelength change command, and communication is established between the OLT (OLT of CO-B) and the outside-area ONU (ONU #1-1' in the CO-A area).

(7) After the permission period ends, the OLT that issued the request for out-of-area communication (OLT of CO-B) and the OLT that received the request for out-of-area communication (OLT of CO-A) each return to the state they were in before the request.

(8) The OLT (OLT of CO-A) that issued permission for communication outside the area sends a command to its subordinate ONU (ONU#1-1') that changed the wavelength in step (6) to return to the original wavelength.

In this way, by changing the wavelength used depending on the UE's location, communication can be carried out without degrading wireless quality even if the UE moves to the area boundary.

In addition, in the above step (4), it is stated that "the OLT that issued the permission for communication outside the area (OLT in CO-A's area) stops outputting its own wavelength during the permission period based on the wavelength controller's correspondence table." In this case, one port of the OLT that issued the permission for communication outside the area (OLT in CO-A's area) and one ONU (ONU#1-1) under the OLT that issued the request for communication outside the area (OLT in CO-B) will not be used.

As shown in the correspondence table in Figure 10(b), the unused wavelengths from step (2) can be used to communicate between one port of the OLT (OLT in the CO-A area) and ONU#1-1, making it possible to make effective use of communication resources. Wavelength adjustments for both devices (one port of the OLT and ONU#1-1) are achieved using the same procedures as steps (5) to (8).

However, in cases where communication resources are to be used effectively, if the wavelength change process is interrupted due to equipment failure or the like, two OLTs may communicate with one ONU simultaneously, causing interference between optical signals and degrading the quality of the wireless signal. To avoid this, in step (4), the OLT that received permission for communication outside the area (OLT of CO-B) further has the function of notifying the OLT that issued permission for communication outside the area (OLT of CO-A) that the wavelength has been switched after the wavelength switch. The OLT that receives this notification (OLT of CO-A) determines that the wavelength change of the OLT that issued permission for communication outside the area (OLT of CO-B) has been completed, and uses the changed wavelength itself. On the other hand, if it does not receive a notification that the wavelength has been switched, it stops using the changed wavelength.

In addition, when a user terminal shifts from a state in which it communicates with ANTs under both CO-A and CO-B to a state in which it communicates only with ANTs under one of the COs, if the terminal repeatedly goes back and forth near the boundary, route changes (wavelength changes) associated with line switching may occur frequently, and the signal processing load may increase. Therefore, for example, as shown in FIG. 11, the boundary line when UE#2 connects to ANT#1-1' and ANT#1-2' (ONU#1-1', ONU#1-2') is set to B1, and the boundary line when connecting to ANT#1-1 and ANT#1-2' (ONU#1-1, ONU#1-2) is set to B2. By setting the positional conditions when leaving the area of a certain ANT wider than the positional conditions when entering, frequent route switching is suppressed and the signal processing load is reduced.

In addition, if two relay stations (RNs) are connected via one PtP connection route, there is a concern that the signal quality improvement effect at the cell edge will be lost if the optical fiber is cut, etc. In that case, as shown in Figure 12, by connecting via two PtP connection routes from the relay station, or by connecting multiple relay stations in a ring configuration, it is possible to realize a highly reliable network without degradation of signal quality even if an optical fiber is cut, etc.

Second Embodiment
The configuration patterns in this embodiment are as follows.
[1] Connection method between OLT and outside area ONU: Always-on connection [2] PtMP implementation method: WDM-PON
[3] Additional access fiber configuration: PtP fiber additional configuration

First, an overview of the optical fiber communication system according to this embodiment will be described. FIG. 13 is a diagram showing an overview of the optical fiber communication system according to the second embodiment. In this embodiment, as in the first embodiment, as an example, an environment will be described in which the ANT to which the UE is connected changes (beam forming #1 → beam forming #2) depending on the area location of the UE shown in FIG. 3, but the present invention is not limited to this.

A relay station is provided to accommodate the base station antenna groups optically connected to accommodating stations CO-A and CO-B, using a single access fiber to accommodate point to multi-point (PtMP). The relay station uses passive components such as AWG and WDM CPL to allocate the optical signal's destination site by wavelength. The ANT site near the border between the CO-A and CO-B areas has multiple O/E (ONU) units so that downstream signals from CO-A and CO-B can be received simultaneously. The ONU site near the border between the CO-A and CO-B areas has multiple E/O (ONU) units so that upstream signals can be transmitted simultaneously to CO-A and CO-B. The configuration of each piece of equipment is explained in detail below.

[Configuration of each device in the optical fiber communication system]
(Accommodation station)
14 is a diagram showing a schematic configuration of a accommodating station CO-B according to the second embodiment. The accommodating station CO-B is an accommodating station that communicates not only with ONU#1-1 in the CO-B area, but also with ONU#1-1' that is always in the CO-A area. The accommodating station CO-B includes a BS and an OLT.

The BS has a BS pool consisting of multiple BSs or BS functions, and connection ports (BS Ports) for multiple BSs or BS functions. In FIG. 14, as an example, a configuration is shown assuming that there are m base stations (number of base station functions) and n number of ports connected to each base station. The OLT has a TRx (Transceiver), AWG (Array Waveguide Gratings), and WDM CPL (Wavelength division multiplexing Coupler).

In this embodiment, a transmission channel (wavelength) independent of communication with ONUs in CO-B is assigned for communication with ONU#1-1'. Therefore, BS Port #1-1'r and TRx#1-1'r are provided in the BS and OLT for communication with ONU#1-1', and wavelengths λ _d1-1 'r and λ _u1-1 'r are used. When communicating with another ONU in the CO-A area in addition to ONU#1-1', additional functions equivalent to BS Port #1-1'r and TRx#1-1'r are required.

Figure 15 shows an example of wavelength allocation in the second embodiment. Figure 15(a) shows a method of allocating wavelengths grouped together by antenna site and transmission direction. Figure 15(b) shows a method of allocating wavelengths grouped together by transmission direction. In this embodiment, in order to perform wavelength multiplexing transmission in which light of different wavelengths is transmitted through a single optical fiber, in the AWG and WDM CPL, for example, wavelengths are allocated and transmitted as shown in Figure 15.

The basic equipment configuration of accommodating station CO-A is the same as that of accommodating station CO-B. However, because it uses different wavelengths than accommodating station CO-B, the wavelength notation is reversed in Figure 14, with λ notation with and without "'". Also, wavelengths with "r" in the λ notation in Figure 14 represent wavelengths for ONUs in another CO area (outside area ONUs). Also, since accommodating station CO-A communicates with relay station RN-A, it is "From/To RN-A".

(Relay station)
Fig. 16A is a diagram showing a schematic configuration of a relay station RN-B according to the second embodiment. Fig. 16B is a diagram showing a schematic configuration of a relay station RN-A according to the second embodiment. Since the configurations of the relay station RN-B and the relay station RN-A are the same, the configuration of the relay station RN-B will be described with reference to Fig. 16A.

Repeater station RN-B is connected to ONUs and to relay station RN-A in the neighboring area by relay optical fiber. In the AWG and WDM CPL, the transmission destination site of the optical signal is assigned by wavelength. AWG for DL_A and AWG for DL_B are used to WDM multiple signals transmitted between RN-A and RN-B among downstream transmission signals. Therefore, they are not necessary when transmitting only one wavelength. Also, AWG for UL_A and AWG for UL_B are used to WDM multiple signals transmitted between RN-A and RN-B among upstream transmission signals. Therefore, they are not necessary when transmitting only one wavelength. WDM CPL#1-1 and #1-1r use the same optical fiber, but they may be divided into WDM CPL#1-1 and WDM CPL#1-1r and transmitted on separate optical fibers.

In relay station RN-B, in addition to the conventional PON system configuration, the gray parts in Figure 16A are added as new configurations, but both are simple configurations that can be configured using only passive components.

(Antenna site)
Fig. 17(a) is a diagram showing a schematic configuration of each antenna site of the second embodiment. Fig. 17(b) is an image diagram showing the positional relationship between each antenna site and each UE. The antenna sites of this embodiment have different configurations between the antenna site near the area boundary (ONU#1-1', ONU#1-1'r) and the antenna site away from the area boundary (ONU#1-1).

The antenna sites (ONU#1-1', ONU#1-1'r) near the area boundary are equipped with multiple O/Es and E/Os. By providing O/E#1-1' and O/E#1-1'r, downstream signals from CO-A (wavelength λ _d1-1 ') and CO-B (wavelength λ _d1-1 'r) can be received simultaneously. Also, by providing E/O#1-1' and E/O#1-1'r, upstream signals to CO-A (wavelength λ _u1-1 ') and CO-B (wavelength λ _u1-1 'r) can be transmitted simultaneously.

The WDM CPL may be divided into two, WDM CPL#1-1' and WDM CPL#1-1'r, and transmitted over separate optical fibers. The Circulator is a component that separates upstream and downstream transmissions, and may be a switch, etc. Also, the Circulator may not be included in the ONU configuration and may be provided externally.

In this way, by providing multiple O/E (ONU) and multiple E/O (ONU) at an antenna site near the area boundary and enabling a constant connection between the OLT and ONU outside the area, even if the UE moves to the area boundary, communication can be performed without switching the optical wavelength of the accommodating station (CO) or antenna site (ONU, ANT), and without degrading wireless quality.

However, in a configuration where one antenna site transmits and receives signals for multiple areas, there is a concern that different wireless signals may be emitted from and received by the ANT at the same time, resulting in signal degradation due to interference. Therefore, beamforming (BF) control information for each wireless signal is shared over the network, and beamforming is performed based on that information, making it possible to transmit signals without interfering with each other.

In addition, if two relay stations (RNs) are connected via one PtP connection route, there is a concern that the signal quality improvement effect at the cell edge will be lost if the optical fiber is cut, etc. In that case, as shown in Figure 12, by connecting via two PtP connection routes from the relay station, or by connecting multiple relay stations in a ring configuration, it is possible to realize a highly reliable network without degradation of signal quality even if an optical fiber is cut, etc.

[Third embodiment]
The configuration patterns in this embodiment are as follows.
[1] Connection method between OLT and outside area ONU: Switching method (dynamically changing IF at CO, ANT)
[2] PtMP implementation method: Cascade connection [3] Additional access fiber configuration: PtP fiber additional configuration

First, an overview of the optical fiber communication system according to this embodiment will be described. FIG. 18 is a diagram showing an overview of the optical fiber communication system according to the third embodiment. In this embodiment, as in the first embodiment, as an example, an environment will be described in which the ANT to which the UE is connected changes (beam forming #1 → beam forming #2) depending on the area location of the UE shown in FIG. 3, but the present invention is not limited to this.

A relay station is provided to accommodate the base station antenna groups optically connected to accommodating stations CO-A and CO-B, using a single access fiber to accommodate point to multi-point (PtMP). Both the CO-A and CO-B areas communicate using the same IF frequency, and the relay station converts the IFoF signal transmitted from the CO into an electrical signal, and using IF signal separators, frequency converters, etc., separates it into radio signals for each ANT site, and inputs each into the E/O. For upstream transmission, the IFoF signal from each ANT site is converted into an electrical signal, multiplexed on the frequency axis using a frequency converter, etc., and input into the E/O for the CO.

Based on the position of the user terminal, which changes with time (timing), the BS and ONU change the IF setting of the radio signal transmitted over IFoF, and each base station antenna communicates with the accommodating station CO-A or CO-B. Although it has been described that the IF setting change is triggered by the user terminal's position information, the IF setting change may also be triggered by other information held by the user terminal or base station equipment (e.g., wireless communication quality information between the antenna/base station and the user terminal, etc.).

In the optical fiber communication system according to this embodiment, the IF (Intermediate frequency) is dynamically changed at the accommodating station (CO) and antenna site (ONU, ANT) based on the UE's location information (which may be wireless communication quality from each Antenna (ANT) at the UE or the base station), and the RN does not dynamically convert the IF frequency. The configuration of each device and the procedure for changing the IF settings are described in detail below.

[Configuration of each device in the optical fiber communication system]
Each device constituting the optical fiber communication system according to this embodiment will be described.
(Accommodation station)
19 is a diagram showing a schematic configuration of a accommodating station CO-B according to the third embodiment. The accommodating station CO-B communicates not only with ONU#1-1 in the CO-B area, but also with ONU#1-1' in the CO-A area depending on the time. The accommodating station CO-B includes a BS, an OLT, and an IF controller (Intermediate frequency).

The BS has a BS pool consisting of multiple BSs or BS functions, and connection ports (BS Ports) for multiple BSs or BS functions. Figure 19 shows, as an example, a configuration assuming m base stations (number of base station functions) and n number of ports connected to each base station. BS Port #1-1 is connected to the IF controller, and receives information on the IF used by the OLT and ONU from the IF controller. BS Port #1-1 then outputs the IF used by the OLT and ONU based on the received IF information. Regarding the notation of f in Figure 19, those without "'" indicate frequencies (IFs) for ONUs within the area (under CO-B), and those with "'" indicate frequencies (IFs) for ONUs outside the area (under CO-A). The same applies to other figures.

BS Port#1-1 is expected to output either IF f _d1-1 (IF for within the area (CO-B area)) or f _d1-1 ' (IF for outside the area (CO-A area)). For example, when communicating with ONU#1-1 under CO-B, f _d1-1 is output since it is within the area, and when communicating with ONU#1-1' under CO-A, f _d1-1 ' is output since it is outside the area.

In addition, in this embodiment, a transmission channel (IF frequency) different from that for communication with ONUs in CO-B is assigned for communication with ONU#1-1'. Since UL and DL transmit optically at different wavelengths, the IF frequency can be the same for upstream and downstream.

In addition, if BS Port #1-1 communicates with another ONU in the CO-A area in addition to ONU #1-1' depending on the timing, an additional BS port capable of outputting at a different IF for the CO-A area is required, similar to BS Port #1-1.

The OLT is equipped with a Mux, Demux, Transceiver (TRx), and WDM CPL (Wavelength division multiplexing Coupler). The WDM CPL may be included in the TRx. The Mux and Demux functions may be part of the BS side functions. In FIG. 19, the input and output frequencies of each BS port are different from the other ports, but on the BS side, the input and output frequencies between each port may be the same, and frequency conversion functions (Down conv., Up conv.) may be included on the Mux and Demux side.

Figure 20 is a diagram showing an example of the arrangement of IFoF transmission frequencies between CO and RN in the third embodiment. Figures 20(a) and (b) are examples of the arrangement of IFoF transmission frequencies in UL and DL in the in-area (normal operation) mode. Figures 20(c) and (d) are examples of the arrangement of IFoF transmission frequencies in UL and DL in the out-of-area operation mode. As shown in Figures 20(c) and (d), in the out-of-area operation mode, in addition to accommodating the in-area ONUs, CO-B accommodates ONU#1-1' in the CO-A area (ONU#1-1 in the CO-B area in CO-A). When accommodating multiple ONUs outside the area, a concentrated frequency band is assigned to the multiple ONUs outside the area for IFoF transmission.

In actual operation, transmission channels for equipment monitoring and control are also necessary, but we will not describe them here. However, these can be placed on the low frequency side, etc., and frequency-multiplexed with the wireless IF signal for transmission.

The basic equipment configuration of the CO-A accommodating station is the same as that of the CO-B accommodating station. However, since the CO-A accommodating station communicates with the relay station RN-A, it is “From/To RN-A.”

(Relay station)
Fig. 21A is a diagram showing a schematic configuration of a relay station RN-B according to the third embodiment. Fig. 21B is a diagram showing a schematic configuration of a relay station RN-A according to the third embodiment. Since the configurations of the relay station RN-B and the relay station RN-A are the same, the configuration of the relay station RN-B will be described with reference to Fig. 21A.

Repeater station RN-B is connected to ONUs as well as to relay station RN-A in an adjacent area via relay optical fiber. In the relay station, in downstream transmission, the IFoF signal transmitted from the CO is converted to an electrical signal, and using IF signal separators, frequency converters, etc., it is separated into radio signals for each antenna site and input to the E/O respectively. In upstream transmission, the IFoF signal from each antenna site is converted to an electrical signal, multiplexed on the frequency axis using a frequency converter, etc., and input to the E/O for the CO. Due to WDM transmission of DL and UL between RNs, the wavelengths of TRx RN are different. Therefore, for example, O-band is used for optical transmission from RN-B to RN-A, and C-band is used for optical transmission from RN-A to RN-B.

Figure 22 is a diagram showing an example of the arrangement of IFoF transmission frequencies between relay stations (RN-A, RN-B) in the third embodiment. Figure 22(a) is an example of the frequency arrangement when IFoF transmission is performed from RN-A to RN-B, and Figure 22(b) is an example of the frequency arrangement when IFoF transmission is performed from RN-B to RN-A, which is an example of the frequency arrangement when optical transmission is performed by shifting to a lower frequency field. The description of the transmission channels for device monitoring and control is omitted, but they can be arranged on the low frequency side, etc., and frequency multiplexed with the wireless IF signal for transmission.

Figure 23 is a diagram showing an example of the arrangement of IFoF transmission frequencies between RN-B and the ONU/ANT site in the third embodiment. Figures 23(a) and (b) are examples of the arrangement of IFoF transmission frequencies between RN-B and the ONU/ANT site in the intra-area (normal operation) mode, showing an example of the arrangement of IFoF transmission frequencies when optical transmission is performed by shifting to a low frequency band. Figures 23(a) and (b) show an example of the arrangement of IFoF transmission frequencies when shifted to the lowest IF frequency for transmission between CO and RN. The illustration of transmission channels for device monitoring and control is omitted, but they can be arranged on the low frequency side, etc., and frequency-multiplexed with wireless IF signals for transmission.

Figures 23 (c) and (d) show examples of IFoF transmission frequency allocation between RN-B and the ONU/ANT site in the out-of-area operation mode, and show examples of IFoF transmission frequency allocation when IFoF transmission between RN-B and the ONU/ANT site is shifted to a lower frequency band for optical transmission and includes IF signals accommodated in CO-A. Although the description of transmission channels for equipment monitoring and control is omitted, they can be allocated on the lower frequency side, etc., and frequency-multiplexed with wireless IF signals for transmission.

(Antenna site)
The antenna site consists of an ONU and an ANT. The ONU is equipped with a WDM-CPL, an O/E, an E/O, frequency converters, and a circulator, and receives commands to change the downlink RF (Radio frequency) and LO (Local oscillator) frequency to obtain the uplink IF transmitted from the BS. Based on the received LO frequency, it changes its own LO frequency and establishes communication with the BS. The circulator is a component that separates uplink and downlink transmissions, and may be a switch, etc. Also, the circulator may not be included in the ONU configuration and may be provided externally.

Figure 24(a) is a diagram showing the schematic configuration of each antenna site during normal operation (no outside-area communication). Figure 24(b) is an image diagram showing the positional relationship between each antenna site and each UE during normal operation (no outside-area communication). As shown in Figures 24(a) and (b), during normal operation, outside-area communication is not performed, and communication is performed within the same area.

For example, communication is performed with antenna sites (ONU#1-1, ONU#1-2, ONU#1-3, ONU#1-4) in the vicinity of UE#2 and in the CO-B area, and IFoF transmission is performed on the communication path from the antenna sites (ONU#1-1, ONU#1-2, ONU#1-3, ONU#1-4) ⇔ relay station B ⇔ accommodating station B, so that in downstream transmission, IF f _d1-1 (IF of the CO-B area) is output from the O/E of ONU#1-1, and in upstream transmission, IF f _u1-1 (IF of the CO-B area) is input to the E/O of ONU#1-1. Similarly, UE#1-1' communicates with antenna sites (ONU#1-1', ONU#1-2', ONU#1-3', ONU#1-4') in the vicinity of UE#1 and in the CO-A area, and IFoF transmission is performed on the communication path from the antenna sites (ONU#1-1', ONU#1-2', ONU#1-3', ONU#1-4') ⇔ relay station A ⇔ accommodating station A, so that in downstream transmission, IF f _d1-1 (IF of the CO-A area) is output from the O/E of ONU#1-1', and in upstream transmission, IF f _u1-1 (IF of the CO-A area) is input to the E/O of ONU#1-1'.

Figure 25 (a) is a diagram showing the schematic configuration of each antenna site during switching operation (with outside-area communication). Figure 25 (b) is an image diagram showing the positional relationship between each antenna site and each UE during switching operation (with outside-area communication). When switching operation is performed, outside-area communication is performed.

For example, when UE#2 moves near the boundary of the area, the antenna site with which UE#2 communicates changes from ONU#1-1, ONU#1-2 to ONU#1-1', ONU#1-2', and communication outside the area is performed. UE#2 communicates with antenna sites (ONU#1-1', ONU#1-2', ONU#1-3, ONU#1-4) near the boundary of the area. In downstream transmission, the frequency converters change the ONU's (ONU#1-1', ONU#1-2') own LO frequency to f _d1-1 ', which indicates a frequency for use outside the area, so that the RF becomes the desired RF for the input IF, and in upstream transmission, the frequency converters change their own LO frequency to f _u1-1 ', which indicates a frequency for use outside the area, so that the RF becomes the desired RF for the input RF, and the changed antenna site (ONU#1-1', ONU#1-2') performs IFoF transmission on the communication path from antenna site (ONU#1-1', ONU#1-2')⇔relay station A⇔relay station B⇔accommodating station CO-B⇔base station A. On the other hand, ONU#1-1 and ONU#1-2, which no longer communicate with UE#2, may stop inputting and outputting IF signals, or, like ONU#1-1' and ONU#1-2', change their own LO frequencies to f _d1-1 ', which indicates a frequency for use outside the area, for downstream transmission, and to f _u1-1 ', which indicates a frequency for use outside the area, for upstream transmission, and perform IFoF transmission on the communication path from the antenna site (ONU#1-1, ONU#1-2) ⇔ relay station B ⇔ relay station A ⇔ accommodating station CO-A ⇔ base station B.

[IF setting change procedure]
Next, the method of controlling the antenna site used in this embodiment will be described with reference to Figures 18 to 25. As described above, in the areas under the accommodating stations CO-A and CO-B, whose coverage is adjacent to each other, the frequency bands for the ONUs under their respective control and the frequency bands for the ONUs under their respective adjacent areas are separated and transmitted via IFoF (for example, frequency band A is used for the ONUs under their respective control, and frequency band B is used for the ONUs in the adjacent area). Each port of the BS and the ONU are designed to determine the route through which the signal is transmitted by determining the IF to be output.

(1) In the area of CO-B, first, the location information of UE#2 transmitted from UE#2 to the BS or mobile core of the accommodating station CO-B is input to the IF controller of the BS. The location information of UE#2 can be input to the IF controller in the following two ways, but is not limited thereto.
(i) The BS of the accommodating station CO-B directly reads the location information from UE#2, and inputs the read location information of UE#2 to the IF controller.
(ii) The location information management server in the upper network reads the location information of UE#2, and inputs the read location information of UE#2 to the IF controller.

The IF controller holds in advance a correspondence table between the UE's location information and each port output IF of the OLT and ONU. Here, we will explain the correspondence table between the UE's location information and each port output IF of the OLT and ONU.

26 and 27 are tables showing an example of the correspondence between UE location information and each port output IF. Fig. 26(a) is a table summarizing information on IFs output to BS Port #1-1 in CO-B, and Fig. 26(b) is a table summarizing information on IFs output to BS Port #1-1' in CO-A. For example, in Figure 26 (a), when the location information of UE #2 is "1" (normal operation mode), the IF (input IF to E/O in CO) used for downlink transmission is "f _d1-1 " and the IF (Input IF to E/O in ANT site) used for uplink transmission is "f _u1-1 '". When the location information of UE #2 is "101" (outside area operation mode), the IF (input IF to E/O in CO) used for downlink transmission is "f _d1-1 '" and the IF (Input IF to E/O in ANT site) used for uplink transmission is "f _u1-1 '".

On the other hand, when UE#2 is in the out-of-area operation mode, CO-A stops outputting IF to ONUs (ONU#1-1', ONU#1-2') under CO-A and interrupts communication. Therefore, in the out-of-area operation mode in FIG. 26(b), the IF (input IF to E/O in CO) used in downstream transmission is "No output", and the IF (Input IF to E/O in ANT site) used in upstream transmission is "-". In addition, in order to effectively use resources, in the out-of-area operation mode, as shown in FIG. 27(b), the IF (input IF to E/O in CO) used in downstream transmission may be "f _d1-1 '", and the IF (Input IF to E/O in ANT site) used in upstream transmission may be "f _u1-1 '" so that CO-A communicates with ONUs (ONU#1-1, ONU#1-2) under CO-B.

(2) After inputting the location information of UE#2 into the IF controller, the OLT checks the correspondence table. If communicating with an ONU outside the area of accommodating station CO-B (for example, ONU#1-1' in the area of CO-A), the OLT sends a request for out-of-area communication (including communication port information for changing the permitted period and time (timing) for communication use, etc.) to the BS (IF controller) in the area of CO-A that accommodates the ONU outside that area (ONU#1-1').

(3) The BS (IF controller) in the CO-A area that receives the request for out-of-area communication returns the availability and permitted time (timing) to the sending BS (the BS in the CO-B area). Regarding the availability, for example, a rule may be determined in advance that indicates that the request can be accepted if there is a reply from the requested BS within a certain period of time, and that the request cannot be accepted if there is no reply within the certain period of time, but the rules are not limited to this.

(4) The BS (IF controller) that has received permission for out-of-area communication switches the output IF of the BS Port during the permission period (time) based on the IF controller's correspondence table. Then, the BS that issued permission for out-of-area communication (BS in CO-A's area) stops outputting its own IF signal during the permission period based on the IF controller's correspondence table.

(5) The BS that issued the out-of-area communication request (BS of CO-B) sends an LO frequency change command to the out-of-area ONU that will be the new communication destination of that port, along with changing the IF of its own output port, to obtain the desired downstream RF and upstream IF. Note that in steps (4) and (5), the BS that issued the out-of-area communication permission (BS of CO-A) may also issue an LO frequency change command to its subordinate ONUs (ONUs that are outside the area from the perspective of the BS that issued the out-of-area communication request).

(6) The outside-area ONU that receives the LO frequency change command changes its LO frequency to an outside-area frequency (f _d1-1 ', f _u1-1 ') based on the information contained in the LO frequency change command, and communication is established between the BS (BS of CO-B) and the outside-area ONU (ONU #1-1' in the CO-A area).

(7) After the permission period ends, the BS that issued the request for out-of-area communication (the BS of CO-B) and the BS that received the request for out-of-area communication (the BS of CO-A) each return to the state they were in before the request.

(8) The BS that issued permission for out-of-area communication (the BS of CO-A) sends a command to its subordinate ONU (ONU#1-1') that changed its LO frequency in step (6) to return it to its original LO frequency.

In this way, by changing the IF according to the UE's location and transmitting via IFoF, communication can be carried out without degrading wireless quality even if the UE moves to the area boundary.

In addition, in the above step (4), it is stated that "the BS that issued the permission for out-of-area communication (the BS in CO-A's area) stops outputting its own IF signal during the permission period based on the IF controller's correspondence table." In this case, one port of the BS that issued the permission for out-of-area communication and one ONU under the BS that issued the out-of-area communication request will not be used.

Therefore, just as with the port of the BS that made the out-of-area communication request, the port of the BS that accepted the request also changes the frequency to the IF (f _d1-1 ', f _u1-1 ') for out-of-area communication based on the correspondence table, making it possible to effectively utilize the ONU that will no longer be used. The IF adjustment is achieved by the same process as (5) to (8).

In this embodiment, as in the first embodiment, when a user terminal shifts from a state in which it communicates with ANTs under both accommodating stations CO-A and CO-B to a state in which it communicates only with ANTs under one of the COs, if the terminal repeatedly travels back and forth near the boundary, route changes (IF changes) associated with line switching will occur frequently, and the signal processing load may increase. Therefore, as shown in Figure 11, the position conditions when leaving an ANT's area are set wider than the position conditions when entering the area, thereby preventing frequent route switching and reducing the signal processing load.

In addition, if two relay stations (RNs) are connected via one PtP connection route, there is a concern that the signal quality improvement effect at the cell edge will be lost if the optical fiber is cut, etc. In that case, as shown in Figure 12, by connecting via two PtP connection routes from the relay station, or by connecting multiple relay stations in a ring configuration, it is possible to realize a highly reliable network without degradation of signal quality even if an optical fiber is cut, etc.

[Fourth embodiment]
The configuration patterns in this embodiment are as follows.
[1] Connection method between OLT and outside area ONU: Always-on connection [2] PtMP implementation method: Cascade connection [3] Additional access fiber configuration: PtP fiber additional configuration

First, an overview of the optical fiber communication system according to this embodiment will be described. FIG. 28 is a diagram showing an overview of the optical fiber communication system according to the fourth embodiment. In this embodiment, as in the first embodiment, as an example, an environment in which the ANT to which the UE is connected changes (beam forming #1 → beam forming #2) depending on the area location of the UE shown in FIG. 3 will be described, but the present invention is not limited to this.

A relay station is provided to accommodate the base station antenna groups optically connected to accommodating stations CO-A and CO-B, each using a single access fiber to accommodate point-to-multipoint (PtMP). Both the CO-A and CO-B areas communicate using the same IF frequency, and the relay station converts the IFoF signal transmitted from the CO into an electrical signal, and using IF signal separators, frequency converters, etc., separates it into radio signals for each ANT site, and inputs each into the E/O. For upstream transmission, the IFoF signal from each ANT site is converted into an electrical signal, multiplexed on the frequency axis using a frequency converter, etc., and input into the E/O for the CO.

In this embodiment, in IFoF transmission between a CO and a relay station, an IF signal for the CO and an ANT within the area and an IF signal for another area are frequency-multiplexed and transmitted via IFoF. In IFoF transmission between relay stations, a downstream IF signal for an area outside a certain CO and an upstream IF signal for a CO outside that area are frequency-multiplexed and transmitted via IFoF. IF signals for the two areas are frequency-multiplexed and transmitted to an ANT site located near the border between the CO-A and CO-B areas. At the ANT site, each IF signal is separated, converted to RF, and radiated from the ANT. In the case of upstream, the RF signals from the two areas are IF-multiplexed on the frequency axis at the ANT site and transmitted. The configuration of each device is specifically described below.

[Configuration of each device in the optical fiber communication system]
(Accommodation station)
29 is a diagram showing a schematic configuration of a accommodating station CO-B according to the fourth embodiment. The accommodating station CO-B is an accommodating station that communicates not only with ONU#1-1 in the CO-B area, but also with ONU#1-1' that is always in the CO-A area. The accommodating station CO-B includes a BS and an OLT.

The BS has a BS pool consisting of multiple BSs or BS functions, and connection ports (BS Ports) for multiple BSs or BS functions. Figure 29 shows, as an example, a configuration assuming the number of base stations (number of base station functions) is m, and the number of ports connected to each base station is n.

In this embodiment, a transmission channel (IF frequency) independent of communication with ONU#1-1' is assigned for communication with ONU#1-1'. Therefore, BS Port #1-1'r is provided for communication with ONU#1-1', and IF f _d1-1 'r and f _u1-1 'r are used. Since optical transmission is performed with different wavelengths in UL and DL, the IF frequency may be the same for uplink and downlink. Regarding the notation of f in FIG. 29, the one without "'" indicates the frequency (IF) for ONU in the area (under CO-B), and the one with "'" indicates the frequency (IF) for ONU outside the area (under CO-A). The same applies to other figures. In addition to ONU#1-1', when communicating with another ONU in the CO-A area, a function equivalent to BS Port#1-1'r is additionally required.

In addition, in this embodiment, a transmission channel (IF frequency) different from that for communication with ONUs in CO-B is assigned for communication with ONU#1-1'. Since UL and DL transmit optically at different wavelengths, the IF frequency can be the same for upstream and downstream.

The OLT is equipped with a Mux, Demux, Transceiver (TRx), and WDM CPL (Wavelength division multiplexing Coupler). The WDM CPL may be included in the TRx. The Mux and Demux functions may be part of the BS side functions. In FIG. 29, the input and output frequencies of each BS port are different from the other ports, but on the BS side, the input and output frequencies between each port may be the same, and frequency conversion functions (Down conv., Up conv.) may be included on the Mux and Demux side.

Figures 30(a) and (b) are diagrams showing an example of the arrangement of IFoF transmission frequencies between CO and RN in the fourth embodiment. Figures 30(a) and (b) show an example of the arrangement of IFoF transmission frequencies in UL and DL when, in addition to accommodating ONUs within the area, CO-B accommodates ONU#1-1'r of CO-A, and CO-A accommodates ONU#1-1r of CO-B. When accommodating multiple ONUs outside the area, a consolidated frequency band is assigned to the multiple ONUs outside the area.

In actual operation, transmission channels for equipment monitoring and control are also necessary, but we will not describe them here. However, these can be placed on the low frequency side, etc., and frequency-multiplexed with the wireless IF signal for transmission.

The basic equipment configuration of the CO-A accommodating station is the same as that of the CO-B accommodating station. However, the IF with an "r" in the description of "f" in Figure 29 indicates an IF for ONUs in another CO area. In addition, the CO-A accommodating station is "From/To RN-A" because it communicates with the relay station RN-A.

(Relay station)
Fig. 31A is a diagram showing a schematic configuration of a relay station RN-B according to the fourth embodiment. Fig. 31B is a diagram showing a schematic configuration of a relay station RN-A according to the fourth embodiment. Since the configurations of the relay station RN-B and the relay station RN-A are the same, the configuration of the relay station RN-B will be described with reference to Fig. 31A.

Relay station RN-B is connected to the ONUs as well as relay station RN-A in the adjacent area via relay optical fiber. In the relay station, in downstream transmission, the IFoF signal transmitted from the CO is converted into an electrical signal, and using IF signal separation equipment, frequency conversion equipment, etc., it separates it into radio signals for each antenna site and inputs them into the E/O respectively. In upstream transmission, the IFoF signal from each antenna site is converted into an electrical signal, multiplexed on the frequency axis using a frequency converter, etc., and input into the E/O for the CO.

Furthermore, in the relay station of this embodiment, in IFoF transmission between the CO and the relay station, the IF signal intended for the CO and the antenna site within the area and the IF signal intended for another area are frequency multiplexed and transmitted via IFoF.

In IFoF transmission between relay stations, the downstream IF signal for outside the area of a certain CO and the upstream IF signal for outside that area are frequency multiplexed and transmitted over IFoF.

IF signals for the two areas are frequency multiplexed and transmitted to an antenna site near the border between the CO-A and CO-B areas. At the antenna site, each IF signal is separated, converted to RF, and radiated from the antenna site. For upstream transmissions, RF signals from the two areas are IF multiplexed on the frequency axis at the antenna site and transmitted.

Due to WDM transmission of DL and UL between RNs, the wavelengths of TRx RN are different. Therefore, for example, O-band is used for optical transmission from RN-B to RN-A, and C-band is used for optical transmission from RN-A to RN-B.

Figure 32 is a diagram showing an example of the arrangement of IFoF transmission frequencies between relay stations (RN-A, RN-B) in the fourth embodiment. Figure 32(a) is an example of the frequency arrangement when IFoF transmission is performed from RN-A to RN-B, and Figure 32(b) is an example of the frequency arrangement when IFoF transmission is performed from RN-B to RN-A, which is an example of the frequency arrangement when optical transmission is performed by shifting to a lower frequency field. The transmission channels for device monitoring and control are not shown, but they can be arranged on the lower frequency side, etc., and frequency-multiplexed with the wireless IF signal for transmission.

Figure 33 is a diagram showing an example of the arrangement of IFoF transmission frequencies between RN-B and the ONU/ANT site in the fourth embodiment. Figures 33(a) and (b) show an example of the arrangement of IFoF transmission frequencies between RN-B and the ONU/ANT site within an area (not including IF signals accommodated in other areas), and show an example of the arrangement of IFoF transmission frequencies when shifted to a low frequency band for optical transmission. Figures 33(a) and (b) show an example of the arrangement of IFoF transmission frequencies when shifted to the lowest IF frequency for transmission between CO and RN. The description of transmission channels for equipment monitoring and control is omitted, but they can be arranged on the low frequency side, etc., and frequency-multiplexed with wireless IF signals for transmission.

Figures 33 (c) and (d) show examples of IFoF transmission frequency allocation when including IF signals accommodated in CO-A. Although the illustration of transmission channels for equipment monitoring and control is omitted, they can be allocated on the low frequency side, etc., and frequency-multiplexed with wireless IF signals for transmission.

(Antenna site)
FIG. 34(a) is a diagram showing a schematic configuration of each antenna site of the fourth embodiment. FIG. 34(b) is an image diagram showing the positional relationship between each antenna site and each UE. The antenna sites of this embodiment have different configurations between an antenna site near the area boundary (ONU#1-1', ONU#1-1'r) and an antenna site away from the area boundary (ONU#1-1). Each antenna site is composed of an ONU and an ANT, and the ONU has a WDM-CPL, an O/E, an E/O, Frequency converters, and a Circulator.

In the antenna site (ONU#1-1', ONU#1-1'r) near the area boundary, in downstream transmission, IF signals ( _fd1-1 ', _fd1-1'r ) for two adjacent areas are frequency-multiplexed and transmitted from the RN to the antenna site near the area boundary, and each IF signal is separated at the antenna site, converted to RF, and radiated from the ANT. Conversely, in upstream transmission, RF signals from the two areas are IF-multiplexed ( _fd1-1 ', _fd1-1'r ) on the frequency axis at the antenna site and transmitted to the RN. The Circulator is a component that separates upstream and downstream transmissions, and may be a switch or the like. The Circulator may not be included in the configuration of the ONU, but may be provided externally.

In downstream transmission, an antenna site (ONU#1-1) away from the area boundary transmits an IF signal (f _d1-1 ) for the CO-B area, converts it to RF at the antenna site, and radiates it from the ANT. Conversely, in upstream transmission, the RF signal from the CO-B area is converted to an IF signal (f _u1-1 ) at the antenna site and transmitted via IFoF.

In this way, by frequency-multiplexing and transmitting IF signals at antenna sites near the area border and enabling a constant connection between the OLT and ONUs outside the area, even if the UE moves to the area border, it can communicate without switching the IF of the accommodating station (CO) or antenna site (ONU, ANT) and without degrading wireless quality.

However, in a configuration where one ANT site transmits and receives signals for multiple areas, different wireless signals are emitted from and received by the ANT at the same time, which raises concerns about signal degradation due to interference. By sharing the beamforming (BF) control information for each wireless signal via the network and performing BF based on that, it becomes possible to transmit signals without interfering with each other.

In addition, if two relay stations (RNs) are connected via a single PtP connection route, there is a concern that the signal quality improvement effect at the cell edge will be lost if the optical fiber is cut or the like. By connecting from the relay station via two PtP connection routes, or by connecting multiple relay stations in a ring configuration, it is possible to realize a highly reliable network without degradation of signal quality even if an optical fiber is cut or the like occurs.

[Fifth embodiment]
The configuration patterns in this embodiment are as follows.
[1] Connection method between OLT and outside area ONU: Switching method (IF is dynamically changed by RN)
[2] PtMP implementation method: Cascade connection [3] Additional access fiber configuration: PtP fiber additional configuration

First, an overview of the optical fiber communication system according to this embodiment will be described. FIG. 35 is a diagram showing an overview of the optical fiber communication system according to the fifth embodiment. In this embodiment, as in the first embodiment, as an example, an environment in which the ANT to which the UE is connected changes (beam forming #1 → beam forming #2) depending on the area location of the UE shown in FIG. 3 will be described, but the present invention is not limited to this.

Both the CO-A and CO-B correspond to the same IF frequency and transmit signals via IFoF (Intermediate frequency over fiber). In the optical fiber communication system according to the present embodiment, the RN dynamically changes the IF (Intermediate frequency) based on the UE's location information (wireless communication quality from each Antenna (ANT) or base station at the UE), and the CO and antenna site use fixed IF frequencies (f _d1-1 , f _u1-1 ). The IF controller of the CO generates IF change information for the RN and transmits it via IFoF together with the radio signal. The configuration of each device and the IF change procedure are described below in detail.

[Configuration of each device in the optical fiber communication system]
Each device constituting the optical fiber communication system according to this embodiment will be described.
(Accommodation station)
36 is a diagram showing a schematic configuration of a accommodating station CO-B according to the fifth embodiment. The accommodating station CO-B communicates not only with ONU#1-1 in the CO-B area, but also with ONU#1-1' in the CO-A area depending on the time. The accommodating station CO-B includes a BS, an OLT, and an IF controller (Intermediate frequency).

The BS has a BS pool consisting of multiple BSs or BS functions, and multiple connection ports (BS Ports) for the BSs or BS functions. A fixed frequency IF signal is output from each BS Port. As an example, Figure 36 shows a configuration assuming m base stations (number of base station functions) and n number of ports connected to each base station. Regarding the notation of frequency f in Figure 17, those without "'" indicate frequencies (IF) for ONUs within the area (under CO-B), and those with "'" indicate frequencies (IF) for ONUs outside the area (under CO-A). The same applies to other figures.

The IF controller holds a table summarizing UE position information, output destination at the relay station RN, and output IF. The IF controller transmits control signals on a transmission channel (IF frequency) separate from the wireless communication signal for frequency conversion control within the RN. Information (control signals) may also be transmitted using other monitoring or control channels. Since UL and DL transmit optically at different wavelengths, the IF frequency may be the same for upstream and downstream.

The OLT is equipped with a Mux, Demux, Transceiver (TRx), and WDM CPL (Wavelength division multiplexing Coupler). The WDM CPL may be included in the TRx. The Mux and Demux functions may be part of the BS side functions. In the figure, the input and output frequencies of each BS port are different from the other ports, but on the BS side, the input and output frequencies between each port may be the same, and frequency conversion functions (Down conv., Up conv.) may be included on the Mux and Demux side. The Mux, Demux, TRx, and WDM CPL are the same as those used in existing cascade connections, so their operation will not be explained here.

In actual operation, transmission channels for equipment monitoring and control are also necessary, but we will not describe them here. However, these can be placed on the low frequency side, etc., and frequency-multiplexed with the wireless IF signal for transmission.

Figure 37 shows an example of the arrangement of IFoF transmission frequencies between CO and RN in the fifth embodiment, and shows an example of the arrangement of IFoF transmission frequencies when accommodating ONUs within the area, as well as ONUs #1-1' in the CO-A area on CO-B and ONUs #1-1 in the CO-B area on CO-A. In UL and DL, when accommodating ONUs outside the area, IFoF transmission is performed at the same IF as when accommodating ONUs within the area, and the IF control channel is placed on the low frequency side. The description of the transmission channels for device monitoring and control is omitted, but they may be placed on the low frequency side, etc. and transmitted together with the wireless IF signal.

The basic equipment configuration of the CO-A accommodating station is the same as that of the CO-B accommodating station. However, since the CO-A accommodating station communicates with the relay station RN-A, it is “From/To RN-A.”

(Relay station)
Fig. 38A is a diagram showing a schematic configuration of a relay station RN-B according to the fifth embodiment. Fig. 38B is a diagram showing a schematic configuration of a relay station RN-A according to the fifth embodiment. Since the configurations of the relay station RN-B and the relay station RN-A are the same, the configuration of the relay station RN-B will be described with reference to Fig. 38A.

Relay station RN-B is connected to ONUs as well as relay station RN-A in the adjacent area via relay optical fiber. Relay station RN-B changes the destination (ONU, BS, another RN) and IF frequency of each IF signal. The relay station is equipped with an IF controller_r, which receives control signals from the BS IF controller, and the IF controller_r controls the frequency converter, Mux, and Demux to change the frequency of the output IF signal from the BS port at the RN site based on the correspondence table in the BS IF controller, and input it to the TRx for the opposing RN site and the subordinate ONUs.

Figure 39 is a diagram showing an example of the arrangement of IFoF transmission frequencies between relay stations (RN-A, RN-B) in the fifth embodiment. Figure 39(a) is an example of the frequency arrangement when IFoF transmission is performed from RN-A to RN-B, and Figure 39(b) is an example of the frequency arrangement when IFoF transmission is performed from RN-B to RN-A, which is an example of the frequency arrangement when optical transmission is performed by shifting to a lower frequency field. The description of the transmission channels for equipment monitoring and control is omitted, but they can be arranged on the low frequency side, etc., and frequency multiplexed with the wireless IF signal for transmission.

Figure 40 is a diagram showing an example of the arrangement of IFoF transmission frequencies between RN-B and the ONU/ANT site in the fifth embodiment. Figures 40(a) and (b) show an example of the arrangement of IFoF transmission frequencies between RN-B and the ONU/ANT site in the intra-area (normal operation) mode, and show an example of the arrangement of IFoF transmission frequencies when optical transmission is performed by shifting to a lower frequency band. Figures 40(a) and (b) show an example of the arrangement of IFoF transmission frequencies when shifted to the lowest IF frequency for transmission between CO and RN.

(Antenna site)
The antenna site consists of an ONU and an ANT. The ONU is equipped with a WDM-CPL, an O/E, an E/O, frequency converters, and a circulator, and receives commands to change the downlink RF (Radio frequency) and LO (Local oscillator) frequency to obtain the uplink IF transmitted from the BS. Based on the received LO frequency, it changes its own LO frequency and establishes communication with the BS. The circulator is a component that separates uplink and downlink transmissions, and may be a switch, etc. Also, the circulator may not be included in the ONU configuration and may be provided externally.

Figure 41 (a) is a diagram showing the schematic configuration of each antenna site during normal operation (no outside-area communication). Figure 41 (b) is an image diagram showing the positional relationship between each antenna site and each UE during normal operation (no outside-area communication). As shown in Figures 41 (a) and (b), during normal operation, outside-area communication is not performed, and communication is performed within the same area.

For example, UE#2 communicates with antenna sites (ONU#1-1, ONU#1-2, ONU#1-3, ONU#1-4) in the vicinity of UE#2 and in the CO-B area, and IFoF transmission is performed on the communication path from the antenna sites (ONU#1-1, ONU#1-2, ONU#1-3, ONU#1-4) ⇔ relay station B ⇔ accommodating station B, so that in downstream transmission, IF f _d1-1 (IF of the CO-B area) is output from the O/E of ONU#1-1, and in upstream transmission, IF f _u1-1 (IF of the CO-B area) is input to the E/O of ONU#1-1. Similarly, UE#1-1' communicates with antenna sites (ONU#1-1', ONU#1-2', ONU#1-3', ONU#1-4') in the vicinity of UE#1 and in the CO-A area, and IFoF transmission is performed on the communication path from the antenna sites (ONU#1-1', ONU#1-2', ONU#1-3', ONU#1-4') ⇔ relay station A ⇔ accommodating station A, so that in downstream transmission, IF f _d1-1 (IF of the CO-A area) is output from the O/E of ONU#1-1', and in upstream transmission, IF f _u1-1 (IF of the CO-A area) is input to the E/O of ONU#1-1'.

Figure 42 (a) is a diagram showing the schematic configuration of each antenna site during switching operation (with outside-area communication). Figure 42 (b) is an image diagram showing the positional relationship between each antenna site and each UE during switching operation (with outside-area communication). When switching operation is performed, outside-area communication is performed.

For example, when UE#2 moves near the boundary of the area, the antenna site with which UE#2 communicates changes from ONU#1-1, ONU#1-2 to ONU#1-1', ONU#1-2', and communication outside the area is performed. UE#2 communicates with antenna sites (ONU#1-1', ONU#1-2', ONU#1-3, ONU#1-4) near the boundary of the area. In this embodiment, the IF is dynamically changed in the RN, so a fixed IF frequency is used at the antenna site. Based on the IF change in the RN, IFoF transmission is performed on the communication path from the antenna site (ONU#1-1', ONU#1-2') ⇔ relay station A ⇔ relay station B ⇔ accommodating station CO-B ⇔ base station A. On the other hand, ONU#1-1 and ONU#1-2, which are no longer communicating with UE#2, may stop outputting IF, or, like ONU#1-1' and ONU#1-2', may perform IFoF transmission on the communication path from antenna site (ONU#1-1, ONU#1-2) ⇔ relay station B ⇔ relay station A ⇔ accommodating station CO-A ⇔ base station B based on the IF change in RN.

[IF setting change procedure]
Next, the method of controlling the antenna site used in this embodiment will be described with reference to Figures 35 to 42. In areas under the accommodating stations CO-A and CO-B, whose coverage is adjacent to each other, the frequency is converted at the RN site to a frequency for the ONUs under the accommodating stations CO-A and CO-B, respectively, and IFoF transmission is performed between the RNs or between the RNs and ONUs (for example, the frequency is converted to f1 for the ONUs under the accommodating stations, and fx (f1 < fx) for the ONUs in the adjacent area). It is designed so that the route through which the signal is transmitted is determined by the converted frequency.

(1) In the area of CO-B, first, the location information of UE#2 transmitted from UE#2 to the BS or mobile core of the accommodating station CO-B is input to the IF controller of the OLT. The method of inputting the location information of UE#2 to the IF controller includes, but is not limited to, the following two methods.
(i) The BS of the accommodating station CO-B directly reads the location information from UE#2, and inputs the read location information of UE#2 to the IF controller.
(ii) A location information management server in an upper network reads the location information of UE#2 and inputs the read location information of UE#2 to the IF controller. Note that the IF controller holds in advance a correspondence table between the UE location information, the output destination at the RN (TRx connection destination), and the output IF at the RF.

Here, we will explain the correspondence table between UE location information, output destinations at RN (TRx connection destinations), and output IFs at RF. Figure 43 is a table showing an example of the correspondence between UE location information and input/output IFs at each TRx. Figure 43(a) is a table summarizing information on IFs used for upstream and downstream transmissions related to BS Port#1-1 in CO-B, and Figure 43(b) is a table summarizing information on IFs used for upstream and downstream transmissions related to BS Port#1-1 in CO-A.

In the relay station, when the location information (Location information) of UE#2 is "1" (normal operation mode), it indicates that the IF of "f _d1-1 " is transmitted to TRx#1-1 in downlink transmission and "f _u1-1 " is transmitted to TRx in uplink transmission, and when the location information (Location information) of UE#2 is "101" (outside area operation mode), it indicates that the IF of "f _{d1-1_r} " is transmitted to TRx RN in downlink transmission and "f _{u1-1_r} " is transmitted to TRx in uplink transmission. And, when UE#2 is in the out-of-area operation mode, it indicates that the IF of "f _{d1-1_r} " is transmitted to TRx RN in downlink transmission and "f _{u1-1_r} " is transmitted to TRx_RN in uplink transmission on the CO-A side. When the BS Port#1-1 in CO-B becomes the out-of-area operation mode, the input/output of the BS Port#1-1 in CO-A may be turned off and stopped.

(2) After inputting the location information of UE#2 into the IF controller of the OLT, the OLT checks the correspondence table. If it is to communicate with an ONU outside the area of the accommodating station CO-B (for example, ONU#1-1' in the area of CO-A), the OLT sends a request for out-of-area communication (including the permitted period and time (timing) for communication use, communication port information to be changed, etc.) to the BS (IF controller) for the ONU outside that area (ONU#1-1').

(3) The BS in the CO-A area that receives the request for out-of-area communication returns the availability and permitted time (timing) to the sending BS (the BS in the CO-B area). Regarding the availability, for example, a rule may be determined in advance that indicates that the request can be accepted if there is a reply from the requested BS within a certain period of time, and that the request cannot be accepted if there is no reply within the certain period of time, but the rules are not limited to this.

(4) The BS (IF controller) that has received permission for out-of-area communication sends a control signal to the IF controller (IF controller_r) in the subordinate RN, and the IF controller controls the frequency converter, Mux, and Demux to change the frequency of the output IF signal from the BS port at the RN site based on the correspondence table during the permitted period (time), and input it to the TRx for the opposing RN site. Then, the BS that issued permission for out-of-area communication (BS in CO-A's area) stops outputting the IF signal from the corresponding port during the permitted period.

(5) The BS (IF controller) that issued permission for communication outside the area also transmits a control signal to the IF controller in the subordinate RN in accordance with the control of (4). The IF controller controls the frequency converter, Mux, and Demux, so that the IF signal transmitted from the RN outside the area is input to the TRx for the corresponding subordinate ONU during the permitted period (time).

(6) When the permitted period ends, the IF controller in the RN returns the frequency conversion equipment, Mux, and Demux to their pre-control states. The BS that issued the permitted out-of-area communication resumes output of the IF signal that was stopped. Note that when returning the state once controlled in (4) to (6) to the original state, a control signal that returns the control information to its original state may be used as a trigger.

By changing the IF in this way depending on the UE's location, communication can be carried out without degrading wireless quality even if the UE moves to the area boundary.

In addition, in the above step (4), if the setting is such that "the BS that issued the permission for out-of-area communication (the BS in CO-A's area) stops outputting the IF signal of the corresponding port during the permission period," one port of the BS that issued the permission for out-of-area communication and one ONU under the BS that issued the out-of-area communication request will not be used.

As a result, just like the BS port that made the out-of-area communication request, one port of the BS that accepted the request continues to output an IF signal, and the IF is changed to the IF for the opposing RN at the subordinate RN site, making it possible to effectively utilize the ONU that will no longer be used. The IF adjustment is achieved using the same process as (4) to (6).

In addition, when a user terminal shifts from a state in which it communicates with ANTs under both CO-A and CO-B to a state in which it communicates only with ANTs under one of the COs, if the terminal repeatedly goes back and forth near the boundary, route changes (IF changes) associated with line switching may occur frequently, and the signal processing load may increase. Therefore, for example, as shown in FIG. 11, the boundary line when UE#2 connects to ANT#1-1', #1-2' (ONU#1-1', ONU#1-2') is set to B1, and the boundary line when connecting to ANT#1-1, #1-2 (ONU#1-1, ONU#1-2) is set to B2. By setting the position conditions when leaving the area of a certain ANT wider than the position conditions when entering, frequent route switching is suppressed and the signal processing load is reduced.

In addition, if two relay stations (RNs) are connected via one PtP connection route, there is a concern that the signal quality improvement effect at the cell edge will be lost if the optical fiber is cut, etc. In that case, as shown in Figure 12, by connecting via two PtP connection routes from the relay station, or by connecting multiple relay stations in a ring configuration, it is possible to realize a highly reliable network without degradation of signal quality even if an optical fiber is cut, etc.

As described above, according to this embodiment, it is possible to improve the quality of wireless communication near area boundaries. In addition, it is possible to build an optical fiber communication system with a simple and economical structure that keeps optical fiber costs and installation time short.

1 Optical fiber communication system 11, 21 OLT
13, 23 Relay station 15, 25 ONU
16, 26 ANT
17, 27 Wavelength controller 19, 29 IF controller 31 Relay optical fiber

Claims (6)

An optical fiber communication system including an OLT (Optical Line Terminal) having a group of ONUs including a plurality of ONUs (Optical Network Units) for each predetermined area ,
A plurality of relay stations provided between each of the OLTs and each of the ONU groups ;
a relay optical fiber that optically connects the relay stations in the adjacent areas ,
An optical fiber communication system, wherein each of the OLTs transmits a signal to an ONU under the control of another OLT using the relay optical fiber. Each of the OLTs is arranged in a station that accommodates the OLT, and is connected to a wavelength controller that controls a wavelength when optically communicating with a subordinate ONU;
The optical fiber communication system according to claim 1, characterized in that, when a first OLT determines, based on location information of a terminal device communicating with an ONU under its control, that the terminal device is communicating with an ONU outside the communication area of each ONU under its control, it requests a second OLT accommodating the ONU outside its communication area to switch to an outside-area mode in which communication is performed using the relay optical fiber, and when the second OLT grants the request, the first OLT and the second OLT switch to the outside-area mode, and the wavelength controller of the first OLT or the wavelength controller of the second OLT notifies the ONU under the second OLT that should switch to the outside-area mode of the wavelength to be used in the outside-area mode, and the terminal device communicates with the first OLT via the ONU that has switched to the outside-area mode and the relay optical fiber. The optical fiber communication system according to claim 1, characterized in that the first OLT transmits signals at a wavelength assigned for inter-relay station transmission between any of the ONUs under the control of the second OLT using the relay optical fiber. Each of the OLTs is arranged in a station that accommodates the OLT, and is connected to an IF controller that multiplexes a wireless signal into an optical signal and controls a frequency when performing IFoF communication with a subordinate ONU;
The optical fiber communication system according to claim 1, characterized in that, when a third OLT determines, based on location information of a terminal device communicating with an ONU under its control, that the terminal device is communicating with an ONU outside the communication area of each ONU under its control, it requests a fourth OLT accommodating the ONU outside its communication area to transition to an outside-area mode in which communication is performed using the relay optical fiber, and when the fourth OLT grants the request, the third OLT and the fourth OLT transition to the outside-area mode, and the IF controller of the third OLT or the IF controller of the fourth OLT notifies an ONU under the fourth OLT that should transition to the outside-area mode of the frequency to be used in the outside-area mode, and the terminal device communicates with the third OLT via the ONU that has transitioned to the outside-area mode and the relay optical fiber. The optical fiber communication system according to claim 1, characterized in that the third OLT uses the relay optical fiber to perform IFoF communication with any of the ONUs under the control of the fourth OLT at a frequency assigned for transmission between relay stations. Each of the OLTs includes an OLT-side IF controller that multiplexes a wireless signal into an optical signal and controls a frequency when performing IFoF communication with a subordinate ONU;
Each of the relay stations includes a relay station side IF controller that receives frequency control from each of the OLT side IF controllers,
The optical fiber communication system according to claim 1, characterized in that, when a fifth OLT determines, based on location information of a terminal device communicating with an ONU under its control, that the terminal device communicates with an ONU outside the communication area of each ONU under its control, it requests a sixth OLT accommodating the ONU outside its communication area to transition to an outside-area mode in which communication is performed using the relay optical fiber, and when the sixth OLT grants the request, the fifth OLT and the sixth OLT transition to the outside-area mode, and the OLT-side IF controller of the fifth OLT and the OLT-side IF controller of the sixth OLT notify the relay station-side IF controller of each relay station under its control of the frequency to be used in the outside-area mode, and the terminal device communicates with the fifth OLT via the ONU under the sixth OLT that has transitioned to the outside-area mode and the relay optical fiber.